Vernal Pool Project Final Report: 2011 Nathan Byer 1 Introduction An ephemeral wetland pool within the Anita C. Leight Estuary Center grounds has recently been the focus of recent study. The wetland area is best described as an ephemeral pool situated in a region of higher elevation in the forest. Its close proximity to trails makes it an interesting potential visitor attraction and a convenient subject for research studies. Although Estuary Center staff has done limited surveys of the area, it has not yet been the subject of official investigation and study. Ephemeral wetlands have become an increasingly important topic for ecosystem-level research. In particular vernal pools have become a popular topic for study. However, there is some debate as to what exactly constitutes a vernal pool and what an ecosystem requires to sustain a vernal pool. The classification system proposed by Cowardin et al (1979) and interpreted by Ferren and Fiedler (1993) defines vernal pools as “seasonally flooded emergent wetlands of the palustrine system” (Cowardin et al 1979, Ferren and Fiedler 1993, Keeley and Zedler 1998). In addition, Keeley and Zedler (1998) propose that three key components must be understood in order to define any vernal pool habitat: the source of water, the duration of the wet and dry seasons of that pool, and the timing of those seasons. As such, they define vernal pools as seasonal wetlands that fill by precipitation during optimal temperature periods for plant growth, consequently go through a “waterlogged-terrestrial” stage, and finally experience an extended dry period (Keeley and Zedler 1998). The study of ephemeral pools requires careful consideration of both the biotic and abiotic conditions of the area. Commonly studied abiotic factors include soil quality, water quality, rainfall, depth, volume, and area (Brooks and Hayashi 2002, Brown and Young 2005, Colburn 2008, Whigham and Jordan 2003). Biotic factors that can be studied generally involve species 2 diversity and/or richness of plants and animals in and around the ephemeral pool area (Brown and Young 2005, Colburn 2008, Zedler 2003). Methods Study Site The ephemeral pool lies along the left branch of the Discovery Trail at Anita C. Leight Estuary Center at an elevation of approximately 65 m (Figure 1). The area is between the Joppa Gravelly Sandy Loam and Beltsville Silt Loam soil series (USDA Natural Resources Conservation Service). Maryland Geological Survey geological maps of Harford County indicate that the area is in the Potomac soil series (Figure 9, MGS 1968). The forest surrounding the pool consists primarily of Nyssa sylvatica and Quercus prinus with an understory of Kalmia latifolia and Vaccinium corymbosum. According to Anita C Leight Staff, the pool has been recorded in the park since 1996, when the estuary center was established, and most likely existed before that. In 2011, Anita C. Leight staff and associates observed the pool and noted that it held water from early April to mid-May. No amphibian life was observed during this period. From May through July, the pool area was dry, with very little evidence of water retention in the soil. The only features that differentiated the pool from the rest of the forest were the shallow depression, which was of slightly lower elevation than the immediately surrounding forest, and the nearly complete lack of vegetation within the pool area. Soil Survey Length and width lines were run across the area in order to divide the area into four quadrants. The area within 1.5 m radius of the intersection of these two lines was designated ‘VPC’ or ‘Vernal Pool Center.’ Similarly, the area outside of this area but within the estimated 3 confines of the vernal pool was defined as ‘VPO’ or ‘Vernal Pool Outside’ and the area outside of the confines of the vernal pool was defined as ‘VPF’ or ‘Vernal Pool Forest’ (Figure 1). Three points were randomly selected in each zone by throwing a dart at a two dimensional diagram of the vernal pool. Two core samples were taken at each point; one sample was separated into upper (designated U) and lower (designated B) layers, while the other was kept intact. The samples were all weighed and placed in a drying oven at 60 degrees Celsius for 12 hours. They were then weighed again in order to give a soil moisture content value, and were then homogenized with a mortar and pestle. From these data, bulk density was calculated as well. The ‘U’ and ‘B’ samples were taken to Maryland Geological Survey for Loss on Ignition (LOI) analysis, a test to determine the amount of organic carbon in the sample. The technique used was adapted from Storer (1984). Samples were placed into crucibles and weighed before heating and after one hour at 105 degrees Celsius. The hour long heating ensured that all or nearly all moisture was eliminated from the samples. Afterwards, samples were heated at 360 degrees Celsius for two hours, after which they were weighed again. These pre- and post-LOI weights were used to calculate %LOI values. In addition, approximately 10 µg each of Vanadium Oxide and each of the ‘U’ and ‘B’ soil samples were placed into small aluminum containers, which were then crimped and placed into sample vials. These sample vials were then analyzed for total nitrogen, carbon, and sulfur. The intact core samples (nine in total) were sent to the University of Massachusetts-Amherst soil labs for their standard soil test. This included tests for pH, buffer pH, extractable nutrients, extractable heavy metals, cation exchange capacity, and percent base saturation. 4 Vegetation Transects Two transects were created to study plant diversity. Each transect ran for 50 m, and passed through the vernal pool with start and end points 25 m from the center of the pool. Each transect bisected two quadrants (Figure 2). At every meter along each transect, all species of flora intersecting the vertical plane of that transect point were recorded. Additionally, every 5 m (excluding the center) a one meter by one meter square PVC pipe quadrat was used to estimate density of flora either to the left or right of that point. The decision to place the quadrat either to the left or right of each 5 m mark was made randomly with a coin flip (heads=left, tails=right). When placing the quadrat frame, one side was placed flush with the transect line, and was oriented so that the 5 m mark on the transect line coincided with the halfway point on that side of the frame. All plants rooted within the frame were counted and recorded. Depth measurements Depth measurements were taken every meter along the length and width lines on six dates: August 30 and September 1, 3, 10, 17, and 24. The length line was designated line A-B, where A and B are endpoints, and the width line was designated line C-D, where C and D are endpoints (figure 1). In total, 19 points on line A-B and 13 points on line C-D were measured for depth, including the endpoints. Throughout the course of early September, hurricane Irene and tropical storm Lee caused significant rainfall. In consideration of this atypical rainfall, data on rainfall for each day in August and September were collected for Abingdon, MD from weather.com as a point of comparison for the depth measurement data. Insect survey Insect samples were to be collected from nine 15 cm long by 15 cm wide by 10 cm deep soil samples. Three samples would be collected in each of the three zones described above: VPC, 5 VPO, and VPF. The samples were to be sifted and searched for any insect life. Any insects found in each sample were to be placed in a killing jar. The killing jar consisted of ethyl acetate-soaked cotton swabs towards the bottom of the jar and a cardboard platform above the cotton so that insects would not become entangled in the cotton. Insects would then be placed in vials according to the location in which they were found for later identification. Ground Penetrating Radar The Maryland Geological Survey (MGS) conducted a Ground Penetrating Radar survey on the vernal pool area. This technique uses electromagnetic pulses to detect point source (like stones, small objects) and non-point source (such as layers of dense strata or mineral beds) underground disturbances. Although this technique does not indicate the type or classification of disturbance, it is useful for determining the existence of a disturbance and its approximate size. Results Soil Parameters Soil moisture content values are reported in Figure 3. Values ranged from below 10% to approximately 50%. The highest moisture content was found in sample VPC-2U, and all upper samples (U) had higher moisture contents than the lower sample (B) taken from the same location (i.e. VPC-1U vs. VPC-1B). The Maryland Geological Survey analyzed upper and lower soil samples for carbon, nitrogen, and sulfur. Most U soil samples had much higher nitrogen, carbon, and sulfur than their corresponding B samples (Table 1). Maryland Geological Survey results also included loss on ignition and total carbon percentages (Table 2). These two indicators were found to have a regression coefficient which is within the same range of results in Konen et al (2002) (Figure 4), 6 since a conversion factor of 1.724 is often used to convert organic matter to total carbon (Nelson and Sommers, 1996). The University of Massachusetts soil testing lab provided data on nutrients and pH. Results from the nutrient analysis can be found in Table 3. Iron and Aluminum levels were higher inside the pool than outside the pool, and were particularly high in the VPC (Vernal Pool Center) samples (Table 3).